Heat is never really lost, but is instead transferred or altered in some fashion. Heat can be transferred in three ways:
(i) Conductive Heat: The direct flow through a solid object from hot to cold. For example, when one sticks a hand in the snow, the snow gets warmer and melts and the hand gets colder.
(ii) Convective Heat: The continuous movement of air or water transferring heat. Heat flow is generally never downward when air is warmed. As warm air expands, it becomes less dense and it rises.
(iii) Radiant Heat: The flow of invisible infra-red rays emitting from the surface of an object, due to the heat from within. All objects give off radiant heat, called radiation. Sunshine is a source of radiant energy. Radiation is also the form of heat transfer which most affects the comfort level of buildings, and is the primary source of human discomfort.
Body heat is lost by all three of types of heat transfers.
Radiant energy travels through space without heating the space itself It only turns into heat when it comes into contact with a cooler surface. The longer an object is exposed to radiant heat, the hotter it becomes. Although it is commonly believed that air temperature alone affects human comfort levels, radiant heat transfer can have an equal effect on temperature levels.
Radiant Barrier Technology (RBT) consists of an airspace with one or more of its boundaries functioning as a radiant barrier. Radiant barriers are made of materials that restrict the transfer of infrared radiation across an airspace. This is accomplished by reflecting the radiation that strikes the barriers, and at the same time, not radiating heat energy. A material that inhibits radiative transfer in this manner is said to have a very low emissivity (the relative power of a surface to emit heat by radiation). The lower the emissivity, the better the radiant barrier. For this reason, the barrier can be placed on either upper or lower surfaces of the object. One side reflects while the other side simply decreases the amount of emitted radiation. Moreover, it is not necessary to form airtight seals with radiant barriers.
Radiant heat is the major contributor to the heat load imposed on an athlete by the environment, and excessive exposure to heat will affect even the best conditioned athlete, hindering their performance, and increasing the potential for possible injuries. Convective heat transfer adds to this radiant heat. Heat-protective clothing is currently not used by athletes because such clothing greatly restricts the potential for body heat loss via evaporation. The athlete experiences a heat load which is determined by the time spent on the field, the intensity of play, the clothing worn and the air circulation on the field as well as the environment. If the heat load is sufficiently severe, detrimental effects on the players health and performance will occur. These range from decreased concentration to painful cramps, fainting, heat exhaustion and heatstroke. These signs and symptoms require immediate medical attention. Thermal comfort is determined by: (i) the air temperature, (ii) the median radiant temperature, (iii) air velocity, (iv) humidity in the air, (v) level of activity, and (vi) the clothing an individual is wearing.
Just as an athlete suffers in heat, athletes also suffer in extreme cold. When cold exposure lasts for more than an hour, cooling of the skin and reduced blood flow to the hands, for instance, leads to blunted sensations of touch and pain and loss of dexterity and agility. Numbness, frostbite, and even hypothermia are all possible dangers associated with extreme cold.
Non-freezing cold injuries can occur when conditions are cold and wet (between 32.degree. F. and 55.degree. F.). The most prominent are chilblain and trenchfoot. The most life-threatening is hypothermia. This occurs when deep body (core) temperature falls below 95.degree. F. Hypothermia victims may show no heartbeat, breathing, or response to touch or pain, and untreated, hypothermia can result in death. Symptoms include withdrawn or bizarre behavior, irritability, confusion, slowed or slurred speech, altered vision, uncoordinated movement and unconsciousness. Even mild hypothermia can result in impairment of decision-making abilities. Cold injuries occur whenever air temperature is below freezing (32.degree. F.). Freezing of the skin surface is termed `frostnip`, deeper freezing through the skin and flesh is termed `frostbite`.
If the wind is blowing, an athlete will lose heat faster and will feel colder because the wind is evaporating the moisture on his or her skin, and blows away the layer of warm air around their body. In an open air sport stadium, for example, a 20 mph wind can make a 5.degree. F. day to feel like -31.degree. F.
The human body has biological defense mechanisms to help maintain proper body temperature. These include vasoconstriction (the tightening of blood vessels in the skin to reduce blood flow to conserve body heat) which leads to discomfort, numbness, loss of dexterity and eventually injury and shivering, which increases internal heat production to help offset lost heat. Internal heat production is increased by physical activity. The more physical the activity, the greater the heat production. In fact, heat production during intense exercise is usually sufficient to completely compensate for heat loss in extreme cold. However, high intensity exercise is fatiguing and causes sweating and cannot be maintained for long periods of time.
The majority of heat loss is through the head. In football helmets, for example, there is no insulation present to protect from extreme cold. Presently, players put athletic tape over the ear holes in an attempt to cut down on the cold wind swirling inside their helmet, but this results in a loud noise in the helmet, as well as freezing ears. Because the rear and front of the helmet are open, the tape does nothing to keep the wearer's ears from freezing and does very little to cut down on the noise produced by the wind once it has entered the helmet. This is the extent of cold-weather protection for helmets.
There is thus a need to provide athletes with a wearable device to protect from radiant heat. There is also a need to provide athletes with insulation and protection from extreme cold in their helmets.